On October 23rd 2007, IBM announced enhancements to its high-end storage, the IBM System Storage DS8000 series. This paper shares perspectives on the latest innovations and enhancements incorporated into this highly competitive enterprise-class disk system. These enhancements are in microcode only and most of them will be “free of charge” available to deploy on installed systems as well. The general availability of most of the enhancements is the 7th December 2007.

October 2007 announcements at a glance

DS8000 series

IBM FlashCopy SE is a snapshot-type local replication that consumes much less storage capacity when compared with the full volume FlashCopy.

IBM's System Storage DS8000 October 2007 release enhances performance, functionality, and provides the ability to reduce costs, and simplify storage management. The following enhancements were announced:

IBM FlashCopy SE (“Space Efficient”) is a snapshot-type local replication to complement the “full volume” FlashCopy feature. A “full volume” FlashCopy requires allocation of capacity equal to or greater than the source volume regardless of the number of updates to the source volume. On average, depending on the application, the amount of data on a volume which is modified over a 24 hour period can vary from approximately 5% to approximately 15%. The “space efficient” FlashCopy only consumes capacity to preserve pre-change source volume tracks, and therefore, it requires far less storage capacity in comparison with the “full Volume” copy technique. Users benefit from better storage utilization and lower TCO. Another possibility enabled by SE's small capacity consumption is the ability to create several point-in-time copies (time shifted) with the ability for fast data recovery. In case of data corruption or operator mistake, the recovery can be performed by returning to the last uncorrupted copy. Snapshot capabilities are required for several near Continuous Data Protection (CDP) techniques. The first release of “space efficient” FlashCopy operates at a volume level of granularity and a data set version is planned for 1H08. The SE FlashCopy is licensed, chargeable feature.

Multiple Readers for IBM System Storage z/OS Global Mirror. z/OS Global Mirror a.k.a. XRC was one of first remote copy techniques introduced more than a decade ago. With this technique, data modifications are temporarily stored in a side-file of the cache and retrieved periodically by the host based System Data Mover (SDM). There is only one reader per SDM. Hence, if “emptying” of the side-file falls behind the new modification pace, the host performance may suffer, and in the worst case, a suspension of remote copy operation may occur.

Since the initial introduction of z/OS Global Mirror, many changes have been made in the storage landscape. Some examples are: much larger disk capacities and the ability to execute many more I/O operations per second thanks to the Parallel Access Volumes (PAV) and Multiple Allegiance (MA) features introduced by IBM. This latest enhancement to z/OS Global Mirror introduces Multiple Readers, which divides the side-file into multiple “sub side-files” and allows parallelism for the SDM when emptying these sub side-files. The users of z/OS Global Mirror with DS8000 will benefit from improved performance and fewer disruptions under heavy write load conditions, and as a result, experience significantly better performance particularly in busy z/OS environments.

Dynamic Volume Expansion. One of the most frequent operational disruptions occurs when a volume reaches its maximum capacity. To prevent this many storage administrators tend to over-provision, which lowers storage utilization. The new feature Dynamic Volume Expansion, as its name suggests, is designed to provide the ability to increase the space on a volume non-disruptively. This capability can help simplify storage management and help minimize over-provisioning in planning volume capacities, which, in turn, can help reduce capital and operation expenditures.

Storage Pool Striping (Rotate Extents) allows for striping of data across several RAID groups. The previous versions of the DS8000 supported logical volume striping across physical disks of a single RAID group. The new feature extends this virtualization by optionally striping the data across multiple RAID groups. The track stripe granularity remains unchanged. Striping the data across a larger number of physical disks helps avoid creating hotspots which, in turn, results in improved performance. This is particularly the case for large sequential operations and can help reduce on-going tuning requirements.

IBM System Storage Productivity Center (SSPC) is being introduced to provide an integrated view with a single, centralized point of management and Storage Resource Management (SRM) functionality. It will support IBM (and some non-IBM) storage, including disks and tape products installed in a data center. In the initial release it will support the DS8000 and the SAN Volume Controller (SVC). It is hosted on an IBM System x type of server, preloaded to simplify installations and upgrades. The initially preloaded components include:

Initially , the DS8000 used the Sequential Prefetching in Adaptive Replacement Cache (SARC) algorithm, which is a self-tuning, self-optimizing cache management technique for a wide range of sequential or random workloads. In May 2007, IBM announced new microcode with general availability in July. The major improvement is a new caching algorithm called AMP (Adaptive Multi-stream Pre-fetching), which in addition to the SARC significantly improves performance for common sequential and batch processing workloads. AMP optimizes cache efficiency by incorporating an autonomic, workload-responsive, self-optimizing pre-fetching technology which delivers up to a two-fold increase in the sequential read capacity of RAID-5 arrays, including for smaller-than-maximum configurations. This technique also reduces “pollution” of the cache with unnecessary data compared to usual pre-fetch algorithms.

Announcement impact

The winners are end-users which will gain from the functionality, performance and potential TCO improvements. This announcement will increase the IBM sales ability in competitive situations, in particular selling against EMC’s DMX.

Summary and conclusions

IBM's System Storage DS8000 series is a stable high-end storage system that is well positioned to cover current and future user requirements. The October 2007 announcement complements the existing product with functions such as a snapshot copy capability and dynamic volume expansion. The DS8000 series internal design, based on commercial server technology, has some significant design advantages, allows easy deployment of future enhancements in performance or functionality and also may enable IBM to be competitive with its pricing.

Action Item: The IBM DS8000 should be put on a short list of any high-end storage procurement.

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